Molecular memory and method for making same

ABSTRACT

A molecular memory including a substrate made of silicon; a set of condensers, each condenser including two conductive layers constituting armatures of the condensers and between which is placed a dielectric layer; and a connector to provide electric contacts with external circuits, wherein the dielectric layer comprises at least partially a polymer containing triazole derivatives, a spin transition phenomenon support material or a spin transition molecular complex; and a method for manufacturing a molecular memory including covering a substrate with a conductive layer; coating a dielectric material on the conductive layer; covering the dielectric material with the conductive layer; impregnating by immersion a buffer in an inking solution of hexadecanethiol; drying and washing the impregnated buffer; creating a protective monolayer on the conductive layer by application of the impregnated, dried and washed buffer; and creating a chemical etching on the sample.

The present invention pertains to the field of microelectronics,especially the manufacture of a set of condensers of micrometric ornanometric size for molecular memories or memories based on molecularaggregates.

The present invention pertains more specifically to a molecular memoryconstituted by a substrate, preferably made of silicon, of a set ofcondensers, each condenser comprising two conductive layers constitutingthe armatures of the condensers and between which is placed a dielectriclayer, as well as connection means intended to provide electriccontracts with the external circuits.

The memories used at present are semiconductor memories which usemagnetic or electric fields to write the information. However, theypresent a certain instability and a fortiori are sensitive todisturbances such as the ambient magnetic field or electric field.Moreover, the memory capacity remains relatively limited because of thesize of these memories.

Thus the present invention has the goal of resolving these drawbacks byproposing a memory constituted of condensers of micrometric ornanometric size in order to perform information storage at the molecularscale.

In order to attain this goal, the present memory is of the typedescribed above and it is remarkable in its broadest sense in that thedielectric material is constituted at least partially by a polymercontaining triazole derivatives, a spin transition complex or a supportmaterial of the spin transition phenomenon.

The dielectric material is preferably constituted at least partially bythe compound [Fe(NH₂trz)₃](NO₃)₂, the compound [Fe(Htrz)₂(trz)](NO₃)₂ orthe compound [Fe(NH₂trz)₃](Br)₂.

The dielectric material is advantageously constituted at least partiallyby an alloy of ligands or anions, such as, e.g., the compound[Fe)Htrz)_(3-3x)(NH₂trz)_(3x)](ClO₄).H₂O or the compound[Fe(NH₂trz)₃](NO₃)_(1.7)(BF₄)_(0.4).

According to a first mode of implementation of the invention, thedielectric material is constituted by the polymer mixture containingtriazole derivatives with another polymer in acetonitrile. The mixturein acetonitrile is advantageously constituted by 40% of the polymercontaining the triazole derivatives and 60% of polyvinyl acetate.

According to a second mode of implementation of the invention, thedielectric material is constituted by a mixture either of the spintransition complex with another polymer in the solvent of the spintransition complex or the spin transition phenomenon support materialwith another polymer in the solvent of the material.

In this manner, the spin coating of the polymer containing the triazolederivative, the spin transition complex or the spin transitionphenomenon support material is facilitated.

The armatures are advantageously made of gold.

The present invention also pertains to a method for manufacturing amolecular memory according to the invention, said method comprisingsuccessively a step of covering said substrate (4) with said conductivelayer (9), a step of coating said dielectric material (1) on saidconductive layer (9) and a step of covering said dielectric material (1)with said conductive layer (10), characterized in that said methodfurthermore comprises the following steps:

-   -   a) impregnation by immersion of a buffer in an inking solution        of hexadecanethiol;    -   b) drying and washing of the impregnated buffer;    -   c) creation of a protective monolayer on one of the conductive        layers by application of the impregnated, dried and washed        buffer;    -   d) creation of a chemical etching on the sample obtained after        step c).

The solution which presents a molar concentration comprised between 0.01mol·L⁻¹ and 0.1 mol·L⁻¹ is preferably brought to a temperature comprisedbetween 30° C. and 50° C. to enable the solubilization of the thiolscontained in the inking solution.

The chemical etching advantageously takes place in an aqueous medium atambient temperature so as to not deteriorate the complex and thepolymer.

The buffer is advantageously transparent and of the polydimethylsiloxanetype.

This manufacturing method makes it possible to form the molecular memorywithout altering the polymer containing the triazole derivatives, thespin transition complex or the spin transition phenomenon supportmaterial constituting at least partially the dielectric material (nooxidation, no dissolution, etc.). This method also enables alignment ofthe motifs on multiple levels for the manufacture of complex memorycomponents.

The present invention also pertains to a method of memory storage andinformation reading performed by means of a molecular memory accordingto any one of claims 1 to 10, characterized in that the memory storageand information reading are based on the hysteretic variations in thecapacity and the conductivity of said dielectric material (1).

Better understanding of the invention will be obtained from thedescription below, presented for purely explanatory purposes, of a modeof implementation of the invention with reference to the attachedfigures:

FIG. 1 illustrates a sectional view of a condenser according to theinvention;

FIG. 2 illustrates the steps of the method for the manufacturing of aset of condensers according to the invention;

FIG. 3 illustrates a perspective view of a memory component constitutedby a set of condensers of different sizes obtained according to themethod described in FIG. 2;

FIG. 4 illustrates a hysteresis cycle of the dielectric constantmeasured in a spin transition complex.

The condenser of micrometric or nanometric size according to theinvention, illustrated in FIG. 1, is of the flat condenser typeconstituted by two conductive armatures (2, 3). There is a bottomarmature (3) and a top armature (2), between which is located adielectric material (1). Said bottom armature (3) of said condenserrests on a substrate (4), preferably made of silicon.

In a preferred mode of implementation, said armatures (2, 3) are made ofgold.

Said dielectric material (1) is constituted at least partially by apolymer containing triazole derivatives. This complex is mixed with apolymer of the polyvinyl acetate type in acetonitrile, so as tofacilitate the spin coating of said complex.

In a preferred mode of implementation, said dielectric material (1) isobtained by mixing in acetonitrile 40% of said complex with 60% ofpolyvinyl acetate.

In a first version of the invention, said dielectric material isconstituted by the compound [Fe(NH₂trz)₃](NO₃)₂.

In a second version of the invention, said dielectric material isconstituted by the compound [Fe(Htrz)₂(trz)](NO₃).

In a third version of the invention, said dielectric material isconstituted by the compound [Fe(NH₂trz)₃](Br)₂.

In a final version of the invention, said dielectric material isconstituted by an alloy of ligands or anions such as, e.g., thecompounds [Fe(Htrz)_(3-3x)(NH₂trz)_(3x)](ClO₄).H₂O or[Fe(NH₂trz)₃](NO₃)_(1.7)(BF₄)_(0.4).

Said dielectric material (1) can also be constituted at least partiallyby a spin transition complex, which would be mixed in the synthesissolvent of said complex.

This invention obviously extends to the use of any spin transitionphenomenon support material.

FIG. 2 illustrates the different steps relative to manufacturing amolecular memory constituted by a set of condensers according to theinvention.

According to one mode of implementation, said substrate (4) made ofsilicon, presenting a thickness of 500 μm, is covered by an adhesionlayer of titanium (8) of a thickness of 50 nm, then a layer of gold (9)of a thickness of 50 nm, said layer of gold (9) representing said bottomarmature (3). Said layer of gold (9) is then coated with thecomplex/polymer mixture constituting said dielectric material (1), thecomplex being either a polymer containing the triazole derivatives, or aspin transition molecular complex or a spin transition phenomenonsupport material. Said dielectric material (1) is then covered with alayer of gold (10) of a thickness of 50 nm. The manufacture of said toparmatures (2) of each of said condensers is then conducted via aprotection by micro/nanobuffering of an inking solution (6) composed ofthiols in absolute ethanol (hexadecanethiol).

In order to do this, an elastomer buffer (5) prepared from an initialmold fabricated by conventional microelectronic methods (opticallithography and ionic etching or electronic lithography and ionicetching for the micrometric or electronic lithography motifs and ionicetching for the nanometric motifs) is impregnated by immersion in saidinking solution (6) presenting a concentration of 0.1 mol·L⁻¹. In orderto enable the solubilization of the thiols, said inking solution (6) isbrought to a temperature comprised between 30° C. and 50° C.

After the operations of drying and washing the surface of said buffer(5) with absolute ethanol at a temperature of 60° C. so as to dissolvethe possible crystals that could form after the drying operation, saidbuffer (5) is applied on said layer of gold (10). Thus, in the zones ofcontact between said buffer (5) and said gold layer (10) there aredeposited 0.1 mol·L⁻¹ of molecular ink, thereby forming a molecularlayer which can be very dense, auto-assembled, monomolecular. For thismechanism, the motifs initially inscribed on the mold are replicated onsaid layer of gold (10).

Said gold layer (10) is then subjected to a chemical etching so as toreveal the motifs formed by the thiol monolayers. In order to do this,the previously obtained substrates are plunged at ambient temperatureinto an aqueous medium (7) of the ferri/ferrocyanide type solution. Thereaction takes place at a pH of 12 so as to avoid any risk of formationof HCN and to prevent precipitation of the silicates stemming from thechemical etching of the surface of said substrate (4).

The elastomer used to constitute said buffer (5) ispolydimethylsiloxane, which is also sold under the trade name of Sylgard184. Because of its transparency, it makes possible the alignment of themotifs of said buffer (5) on the motifs preexisting on the sample. Thismakes possible the manufacture of complex devices requiring multiplelevels of lithography.

FIG. 3 illustrates an example of fabrication of a memory componentconstituted by a set of condensers of different sizes obtained byimplementation of the method described above. Said component isconstituted successively of a substrate (4), preferably made of silicon,a layer of gold (9) constituting said bottom armature (3) of saidcondensers, a dielectric material (1) constituted at least partially bya polymer containing triazole derivatives, a spin transition molecularcomplex or a spin transition phenomenon support material, and gold discs(11) of different sizes, each constituting said top armature (2) of acondenser. The exterior surface of at least one of said top armatures(2) is connected by a connection wire to a connection terminal placed ona free part of said substrate (4) in order to provide electric contactswith the external circuits (not represented in FIG. 3).

The molecular component can also be constituted by a set of flatcondensers, with each condenser comprising two armatures of theelectrode type of micrometric or nanometric size, between which isarranged said dielectric material support of spin transition.

The electrodes of said condensers constituting such a molecularcomponent are manufactured by the previously described buffering methodor by any other nanolithography means.

The horizontal architecture of said condensers presents numerousadvantages, especially in terms of addressing and density ofintegration.

Furthermore, the storage of information and the reading of informationcan be based not solely on the hysteretic variations in the capacity butalso on the hysteretic variations in the conductivity of the electricmedium.

FIG. 4 illustrates in an explanatory manner the performance of thedielectric constant measures in the compound [Fe(NH₂trz)₃](NO₃)₂ as afunction of temperature.

The invention was described above as an example. It is understood thatthe expert in the field could implement different variations of theinvention without going beyond the scope of the invention.

1. Molecular memory constituted by a substrate (4), preferably made ofsilicon, of a set of condensers, each condenser comprising twoconductive layers (9, 10) constituting the armatures of said condensersand between which is placed a dielectric layer (1), as well asconnection means intended to provide electric contracts with theexternal circuits, characterized in that said dielectric material (1) isconstituted at least partially by a polymer containing triazolederivatives, a spin transition phenomenon support material or a spintransition molecular complex.
 2. Molecular memory according to claim 1,characterized in that said dielectric material (1) is constituted atleast partially by the compound [Fe(NH₂trz)₃](NO₃)₂.
 3. Molecular memoryaccording to claim 1, characterized in that said dielectric material (1)is constituted at least partially by the compound[Fe(Htrz)₂(trz)](NO₃)₂.
 4. Molecular memory according to claim 1,characterized in that said dielectric material (1) is constituted atleast partially by the compound [Fe(NH₂trz)₃](Br)₂.
 5. Molecular memoryaccording to claim 1, characterized in that said dielectric material (1)is constituted at least partially by an alloy of ligands or anions. 6.Molecular memory according to claim 5, characterized in that saiddielectric material (1) is constituted by the compound[Fe)Htrz)_(3-3x)(NH₂trz)_(3x)](ClO₄).H₂O or the compound[Fe(NH₂trz)₃](NO₃)_(1.7)(BF₄)_(0.4).
 7. Molecular memory according toany one of the preceding claims, characterized in that said dielectricmaterial (1) is constituted by a mixture of said polymer containingtriazole derivatives, of said spin transition complex or said spintransition phenomenon support material with another polymer. 8.Molecular memory according to claim 7, characterized in that saiddielectric material (1) is obtained by the mixture of 40% of saidpolymer containing triazole derivatives and 60% of polyvinyl acetate inacetonitrile.
 9. Molecular memory according to claim 7, characterized inthat said dielectric material (1) is obtained by the mixture of saidspin transition complex with said polymer in the solvent of said spintransition complex, or the mixture of said spin transition phenomenonsupport material with said polymer in the solvent of said material. 10.Molecular memory according to claim 1, characterized in that saidarmatures are made of gold.
 11. Method for manufacturing a molecularmemory according to any one of claims 1 to 10, said method comprisingsuccessively a step of covering said substrate (4) with said conductivelayer (9), a step of coating said dielectric material (1) on saidconductive layer (9) and a step of covering said dielectric material (1)with said conductive layer (10), characterized in that said methodfurthermore comprises the following steps: a) impregnation by immersionof a buffer (5) in an inking solution (6) of hexadecanethiol; b) dryingand washing of the impregnated buffer (5); c) creation of a protectivemonolayer on said conductive layer (10) by application of saidimpregnated, dried and washed buffer (5); d) creation of a chemicaletching on the sample obtained after step c).
 12. Method formanufacturing a molecular memory according to claim 11, characterized inthat said inking solution (6) presents a molar concentration comprisedbetween 0.01 mol·L⁻¹ and 0.1 mol·L⁻¹.
 13. Method for manufacturing amolecular memory according to claim 11 or 12, characterized in that saidinking solution (6) is brought to a temperature comprised between 30° C.and 50° C.
 14. Method for manufacturing a molecular memory according toclaim 11, characterized in that said chemical etching takes place in anaqueous medium (7) at ambient temperature.
 15. Method for manufacturinga molecular memory according to claim 11, characterized in that saidbuffer (5) is transparent.
 16. Method for manufacturing a molecularmemory according to claim 15, characterized in that said buffer (5) ispolydimethylsiloxane.
 17. Method for storage in memory and reading ofinformation, implemented by means of a molecular memory according to anyone of claims 1 to 10, characterized in that the memory storage andinformation reading are based on the hysteretic variations in thecapacity and the conductivity of said dielectric material (1).